In 3GPP, setting up a home base station (Home eNodeB or Home NodeB; referred to, hereinafter, as “HeNB” or “HNB”) and constructing a CSG cell is being studied (refer to Non-patent Document 1). As shown in FIG. 17, the CSG cell is constructed within a cell (macro-cell 1701) constructed by ordinary base stations (eNB). Unlike the eNB, the HeNB is provided with a function enabling restriction of terminals (user equipment; referred to, hereinafter, as “UE”) that are permitted access, and a UE (terminal) can only connect to a CSG cell for which access permission is granted. Excluding emergencies, the UE (terminal) is unable to connect without access permission regardless of a CSG cell with high reception quality being detected.
To verify access permission for a CSG cell, the UE (terminal) is required to verify cell identification information included in notification information transmitted from the CSG cell (base station). Each CSG cell has an ID, referred to as a CSG ID, in group units, and access permission is granted to the UE (terminal) in CSG ID units. The UE (terminal) collates a CSG ID list (access permission list: CSG white list) of accessible CSG cells, notification of which has been received from a network, and the CSG ID that is the cell identification information received from the notification information of the CSG cell, and judges that access is possible if the CSG ID of the detected CSG cell is included in the CSG white list. The CSG ID is referred to, hereinafter, as access permission information.
All cells have cell identification information referred to as a physical cell ID (PCI). Regarding the CSG cell, as shown in FIG. 18, CSG cells having the same PCI may be present near a serving base station 1801 (serving cell) to which the UE (terminal) is currently connected. This is referred to as a PCI collision. The UE (terminal) measures reception quality for signals from near-by cells, and a trigger is performed when the reception quality of the serving base station 1801 or a near-by cell satisfies certain conditions. This is referred to as an event trigger.
When the trigger is performed, the serving base station 1801 receives notification of the PCI of the cell having high reception quality by a measurement result report message (measurement report). Based on the reception quality information, the serving base station 1801 decides a handover destination and transmits a handover request message (handover request; HO request) to the handover destination cell. In this instance, if a PCI collision occurs, the serving base station 1801 may transmit the handover request message (handover request; HO request) to the wrong cell. This is referred to as PCI confusion.
To prevent PCI confusion, the UE (terminal) detects a cell global ID (CGI) that is a unique cell identifier from the notification information of the CSG cell, and notifies the serving base station 1801 of the CGI using the measurement result report message. The serving base station 1801 specifies the CSG cell from the notification. However, time is required to detect the CGI from the notification information. Therefore, first, notification is given of the PCI of the cell having high reception quality and the measured reception quality by a first measurement result report message (1st measurement report). The serving base station 1801 selects one handover destination candidate cell from the cells within the received first measurement result report message. When the selected cell is a CSG cell, to instruct the UE (terminal) to detect the CGI of the CSG cell, the serving base station 1801 transmits a measurement setting message (measurement configuration) including the PCI of the CSG cell and setting information required for detecting the CGI to the UE (terminal).
The UE (terminal) detects system information (SI) including the CGI from the notification information of the CSG cell of which instruction has been given based on the measurement setting message (referred to as SI reading), and performs access verification using the access permission information (CSG ID). Then, the UE (terminal) notifies the serving base station 1801 of the cell information of the CSG cell from the system information and the access verification result after access verification processing by a second measurement result report message (2nd measurement report). In addition, during system information detection, the serving base station 1801 sets a gap or DRX for interrupting data transmission to the UE (terminal), thereby enabling the UE (terminal) to detect the system information of nearby base stations. An example of a sequence of the above-described operation is shown in FIG. 19.
Here, when the access permission information included in the second measurement result report message is “no access permission (non-member)”, a serving base station 2001 gives an instruction, by the measurement setting message, to measure a frequency (e.g. f2) other than the frequency (e.g. f1) supported by the CSG cell (CSG cell 1) of which the UE has given notification, as shown in FIG. 20.